1. Technical Field
The present invention relates in general to computer network communications and in particular to a method and apparatus for interconnecting wide area computer data processing networks with local area computer networks. Still more particularly, the present invention relates to a method and apparatus for interconnecting a wide area computer data processing network with a local area computer network while minimizing the amount of routing information which must be maintained within the wide area computer data processing network.
2. Description of the Related Art
Computer system networks continue to increase in popularity. That is, in large part, because such networks allow applications and users running on many different systems to communicate with each other, providing data and resource sharing. Networks may be limited to a desktop systems located in close physical proximity, or may include thousands of systems of all sizes connected in a worldwide network. In general, networks are flexible, so they may be adapted to suit the needs of their users.
One important type of computer network is referred to as a peer to peer network. With such a network topology each node of the network is considered to be equal with all other nodes. Each node may act as an intermediate node in a communications session, routing sessions between other network nodes. Such networks may also include terminal nodes, which are not required to transmit data between two separate, adjacent systems as part of a communications link between them. A communications session initiated by a node of the network is routed to the nearest node, which selects the routing to be used to the next node in a communications link. One example of such a powerful, flexible system is System Network Architecture (SNA), a network architecture defined by International Business Machines Corporation, and widely used throughout the world.
In a typical network, local networks, or subarea networks are often connected to the remainder of the network through a single, fully featured, network node. Such network nodes must have full routing and functional capability within the network, but terminal nodes, such as workstations, which are connected to a network node need not have such a capability. Even if only a few low end workstations in a single physical location are connected to a wide area network, a system capable of supporting full network node functions must typically be placed locally to allow such network access.
A full network node must be a relatively powerful system capable of supporting a wide variety of network functions. For example, an SNA network node must be capable of acting as an intermediate node in a session between two nodes which may be connected through a large number of additional intermediate nodes. The network node maintains a route selection table for many of the logical units in the network, and has the capability to search for and determine the location of any node within the network given its logical unit identifier. When a logical unit requests a session with another logical unit, a network node receiving such a request must locate the target logical unit, either in its route selection table, or by searching for it, and thereafter establish communication sessions with both the logical unit making the request and a companion session with another adjacent node. The other adjacent node may be the target logical unit, or it may be another intermediate node utilized to establish a link to the target logical unit.
Once a session has been set up between two logical units, the network node routes incoming data to the appropriate outgoing communications link. Various services are provided by the network node. These may include, for example, adaptive pacing of data, renegotiation of bind values, and similar services. The numerous functions required of a network node are well documented, and well known to those skilled in the art.
The complex functions and duties required of a network node are in part due to the requirement that each network node within such a network must have the ability to provide route selection, directory search processing and intermediate routing functions for all nodes within the network. As a result, each network node must maintain a topology database which specifies all interconnected nodes within the network. This topology database is replicated among all network nodes within a data processing network while local address information, such as that found within endpoint nodes, is provided on an as-required basis.
In a large network, network topology databases may grow to a significant amount of data. This in turn can result in significant network performance degradation due to several reasons. The link bandwidth consumed by topology database updates increases substantially as a result of larger databases. As a consequence, user data frames may experience longer and longer delays due to the high transmission priority of network topology database updates.
Additionally, the processing time of route collections increases exponentially as the number of links and networks within a network increases. As a consequence, session set-up time will be substantially lengthened. Additionally, building a large spanning from which routes are chosen requires additional processor capacity. As a result, less processor capacity is available for user applications. Finally, slower reaction times due to failures and slower response times due to increased time to propagate topology database updates and searches through a large network will further degrade the performance of a data processing network.
This problem is increased in severity due to the proliferation of local area networks and the growth of data processing networks in size. For purposes of this application the term xe2x80x9clocal area networkxe2x80x9d is utilized to mean traditional local area networks as well as subregion networks, subarea networks, star networks and other such networks. In networks in which a large number of such local area networks are interconnected by a wide area network, at least one network node within each local area network must be connected to the wide area network. Due to the requirement that the entire network topology must be replicated within every network node within the network, each local area network connected to the wide area network requires three entries to be made in the network topology database which is replicated throughout the network. A specification of the network node and the two bi-directional links associated with that network node must be maintained for each local area network interconnected with a wide area network. Networking then flows through the local area network server into the local area network and intermediate session routing is typically done by the network node acting as the local area network server. In large networks, a local area network server performing the backbone intermediate session routing function is frequently undesirable.
In view of the above, it should be apparent that a need exists for a method of efficient coupling multiple local area networks together with a wide area network while minimizing the amount of routing information which must be maintained within the wide area data processing network.
It is therefore one object of the present invention to provide an improved computer network communications systems.
It is another object of the present invention to provide an improved method and apparatus for interconnecting local area networks with wide area data processing networks.
It is yet another object of the present invention to provide an improved method and apparatus for interconnecting multiple local area networks with wide area data processing networks while minimizing the amount of routing information which must be maintained within the wide area data processing network.
The foregoing objects are achieved as is now described. The method and apparatus of the present invention may be utilized to interconnect multiple local area networks to a data processing network including both multiple network nodes having routing and functional capability within the data processing network and multiple endpoint nodes having only local address capability, while minimizing the amount of routing information which must be maintained within the data processing network. A concentrator node is established for interconnection between each of the multiple local area networks and the data processing network. The concentrator node includes a network node interface having routing and functional capability for an associated local area network and an endpoint node interface having local address capability. When interconnected between a local area network and a selected network node within the data processing network, the concentrator node emulates a network node within the local area network while appearing as an endpoint node within the data processing network, permitting full connectivity between the local area network and the data processing network. The concentrator node maintains routing information for communication between the local area network and the data processing network in two segments. The first segment details the route between the local area network and the concentrator node while a second segment details the route between the concentrator node and a node within the data processing network.